over weight mice

Question
i have two female mice which i've ad for 9months now and one of them just eats and sleeps and has gotten big. what would cause this.she is still active and runs around a lot.

Answer
Dear Tracy,

Some mice just get fat.  It is hereditary.  Assuming they are eating a balanced diet-- probably a mouse mix-- and have a working wheel, and she is active-- I would not worry.  

You can take her to a vet to check her out if you are worried, but the likelihood is that even if there were something wrong (an internal tumor, for instance), nothing could be done.

squeaks,

Natasha